Stress-free stud



O. M. SUMMERS Sept. 10, 1946.

Patentecl Sept. 10, 1946 UNITED STATES PATENT orrrcr.

STRESS-FREE STUD Otto M. Summers, Mount Gileed, Ohio, assignor to H-P-M Development Corporation, Wilmington, Del, a corporation of Delaware Applieation February 16, 1944, Serial No. 522,536

12 Claims. 1

This invention relates to studs and the member in which they are mounted so as to distribute the stress applied upon the stud substantially uniformly throughout the threaded iength thereof. The invention partioulariy re1ates to highly stressed studs, of which one cla-ss is IJOWI1 as prestressed studs that are loaded to the maximurn stress condtion that wi11 normally be received by the stud under any conditions that infiuence the operating mechanisms held by the studs.

One of the major dificulties with studs of the conventional type that are provided with standard threads and are adapted to be threaded into tapped holes is that the stress appiied to the stud to tighten the same in the hole causes a loca.1ized stress in the stud that is located just below the thread line.

In order to re1ieve localized stresses in sinds it has been suggested to provide as neer 109 thread contact of the stud with the threads in the tapped hole for the same as possible, tending to distribute the stress load over as great a number of thre ads as possbie, or to provide special thread designs, er toprovide shoulders on the studs that are brought into engagement with the member in which the stud is supported s as to approagh the stress conditions developed in the ordinary cap screw. A11 of these prior developments are "more or 1ess centered around the maintenance of accurately dimensioned threads on the stud and in the hole to receive the seme so as to obtain as neer as possib1e en aCcurate axial aligmnent of the stud in the hole ahd thereby reiieve any angular stresses set up in the stug1 when it is used to secure one object upon ariother. An object of this ivention is to provide a stud that can be positioned in a, standard tapped hole so that looaiized stresses in the stud are substantiaily eliminated.

Stii1 another object of the invention is to provide a stud in eccordance with the oregong object wherein the stud is threaded into the tapped hole in a relatively free, or floating, condtion so thet but siight etort is required for this operation, and wherein means is assocated with the stud which ceuses all of the threads, of the stud to iricti'cmaily engege the threads of the tapped hole in Which the stud is placed for holding the Same in the hole in iocked condition therein in a marmer that a reiativeiy high torque eifort is required to intially release the stud from the tapped hole, but which when on e released aan be readily removed rom the tapped hole with reiatively litt1e effort.

Stil1 another object of the invention is to pro vide a relativeiy stress free stua mounting arrangement Wherein the threaded portion of the stud may be termed undersize rom standard. thread practice design for threading into a tapped hole that is of standard size according to thread practice design, so that the stud can be free1y threaded into the threaded hole which receives the Same and resilient means is provided for frictionaliy engaging the threads of the stud wth the threads of the hole in whch it is received for thereby preventing removal of the stud from the hole unless a relatively high torque eiort is appiied upon the stud.

Stii1 another object of the invention is to pro- Vide a, stud with an undersize threeded body portion that is inserted in a standard size tapped hole and the resilient washer causes frictional engagement of the stud threads with the hole threads to prevent remova1 of the stud from the hole.

A sti1l further object of the invention is to provide a stud in eccordance with any of the foregong objeots wherein the stress ioad applied upon the stud is distributed over substantially the entire thread iength thereof without cauing any looelization of stresses at the thread line of th stud.

Fnrther objects and advantages wi11 become apparent from the drawing and the f oilowng description.

In the drawings:

Figure 1 is a vertical cross-sectonal view of a meohanism illustrating the use of the stud of this invention or securing mernbers together.

Fgure 2 is a, cross-seetional view illustrating the marmer of mounting a stud accordng to conventional practice.

Figure 3 is a cross-sectional view of a portion of a stud similar to that illustrated in Fgure 1 out showing a, slightiy modified arrangement thereo.

Fgure 4 is a, cross-sectionai view showing a modified arrangement for obtaining en axia1 forse upon the stud of this invention by means of a, plug of rubber-like material.

Aecording to what may be termed conventional stud mounting practice, as iilustrated in Figure 2, a stud body 10 is provided With a, threaded end H thereon that is received in a, threa.ded hole 12 of any suitable mounting member l3. In cutting the threads l l en the stud body In the maximum diameter of the threaded portion is substentialiy the same as the diameter of the stud body, and are out to tolerances allowed by standard thread practice. The threaded hole l2 is also tapped with the threadstherein according to standard thread practice so that When the threaded end l l of the stud is insertedin the, threads of the hole I2 there will be a, certainamount of friotion developed therebetween when the stud ID is threaded into place. When the thread line of the stud reaches the top of the threaded hole i2 it may then be tightened by suitable degree of torque being applied thereon. It has been found in practice that when studs are nserted into a supporting member in this manner that the threaded portion of the stud becomes highly stressed just below the thread line of the stud, generally one or two threads below the thread line. This is probably caused by the degree of misalignment between the threads on the stud and the threads in the supporting member, and by the stress set 119 by the thread line shoulder en the stud engaging the angular surfaces of the threads in the hole whch tend to throw the body of the stud ahgularly relatively to the axis of the hole.

When studs of this nature are placed under a highly stressed conditionand particularl when -the stress is of a cyclic nature, the studs tend to fatigue and crack just below the thread line.

The attempts of correction have been te -accurately size the threads on the stud as well as the threads in the hole whichreceives the same to provide as nearly 100% contact between the threads as possible. This, of course, has entailed careful manufacturing operations and the use of special lubricants in orderto thread the studs into position in their supporting members. On the other hand, various shoulders have been provided on the studs that were adaptd to engage the surface of the supporting member tending to maintain the alignment between the stud and the hole, but even in these instances the major load of the stress upon the stud is carried by the top two orthree threads upon the.stud in the same manner as heretofore referred 120.

In this invention, however, the stud is provicled with a, body portion 2! that has the lower end thereof provided with threads 22. The threads 22 of the stud 20 are received by the threads 23 provided in the tapped hole 24 located in the support member 25 whch may be any suitable device.

The tapped hole 24 is first drilled With a suitable size drill to provide the lead for the tap for tapping the hole. The tap used in tapping the hole which has been previously drilled, is a standard tap for producing threads 23 in the hole 24 according to standard thread practice.

The threads 22 that are cut on the stud 20 are what may be termed undersize threads according to standard thread practice with regard to the size of the threads 23 so that the threads 22 are a relatiVely loose fit within the threads 23. The threads 22 are in practice actually made sufficiently undersize relatively to the threads 23 that the stud 20 can be threaded freely by hand without the use of auxiliary tools. As a. general rule the stud end thread 22 can be undersize on pitoh diameter of 1% ofthe bar size plus .002 inch.

The stud 20 is provided with an undercut portion 26 that is slightly smaller in diameter than the minor or root diameter of the thread 22. In

general this may be stated to he 3% under norma1 or root diameter. The undercut portion 26 is connected with the thread line by a chamfer 4 21 and the sharp corners of the chamfer are broken. By providing the stud 20 with an undercut portion 26 the axial thrust or stress produced in ab1y provided with rounded or chamfered corners 30 to prevent the same from digging into the end of the stud 20 and producing shavings whch may in some Way get into the mechanism that is being assembled by the use of the studs.

The upper end 3| of the stud 20 may b provided with threads 32 produced according to standard thread practice to receive a nut 33 that is threaded according to standard practice to be placed upon the threads 32. The nt 33 secures any desired member 34 upon the member 25, and a suitable metal gasket 35 may be positioned therebetween if desired.

When the stud 20 is to be assembled upon the member 25, the spring look washer 29 is placed in the hole 24 and then the threads22 of the stud 20 are threaded into and received by the threads 23 in the hole 24. When the stud 20 is being threaded downwardly into the hole 24, the undersize threads 22 will thread freely in the threads 23, and actually a slight clearance is provided therebetween. This operation can usually be performed by hand and without the use of auxiliary tools. When the bottom portion 28 of the stud 20 contacts the spring look washer 29 a suitable torque wrench can be applied to the stud 20 whereby to urge the samedownwardly into the hole 24, forcing the end 28 against the spring look washer 29 to 'compress thesame. Compression of the spring look washer 29 urges the upper faces of the threads 22 against the 29 tendingto continuously urge the stud 20 upwardly.

When the stud 20 is ins'erted in the hole 24 in this manner, it will be noted that there will be nosingle point of localized stress in the stud because the looseness of the stud threads in the threads in the hole during insertion of the stud therein permits freedom of movement, or floating movement, of the stud in the hole to permit the threads 22 to engage uniformly the threads 23 of the hole 24. It will be noted that there is no localized stress at the thread line of the stud in the manner heretofore referred to with reference to Figure 2. When the nut 33 is now applied upon the upper threaded end 32 of the stud 20 and tightened with a suitable torque wrench to pre-stress the stud 20 to any desired degree, it will be apparent that the stress load carried by the stud 20 will be distributed over the entire area of the threads 22.

With the threads 22 in frictional engagement gagement between the threads 22 and 23 is maintainecl by the spring lockwasher 29 so that the nut 33 aan he applied and removed from the upper threaded end 32 of the stud without causing rotation of the stud in the hole 24. In faat, in aatual practica it has been found that the studs may be assembled in their holes and the spring look washer 29 aompressed with relatively complet freedom of movement during the assembly operation, and that after the studs have set in postion in their threaded. holes for a relatively short period of time the friational contact between the threads22 and the threads 23 beaome so fgreat that a force substantially greater is required to initially release the stud to remove the same from the hole 24 than was required to place the same in position. However, as soon as the static frozen aonclition between the threads 22 and. 23 is broken, the stud may be rotated relatively freely by means of a wrenah until the end portion 28 of the stud moves pwardly away from the spring look washer 29 to relieve the forae thereof rom the stud 261, and subsequently the stud may be removed from the hole 24 relatively -freely by hand.

In Figure 3 there is shown a slightly modifiecl arrangement of the stud illustrated in Figure 1, and which may be used to adapt the use of the prinaiples of this invention to studs that are used or replacement in existing meahansms.

In general, the stud 4il, shown in Figure 3, haV- ing the threads 4-i thereof, is constructed in the same manner as the stud 2, illustrated in Figure 1, so that the threads 4| thereof engage the threads 42 of the hole 43 in the member 44 in the same manner as heretofore desarbed. However, in this modifiaation the end portion 28 of the stud, as illustrated in Figure 1, is replaaed by a loose pilot member 45 that is inserted in the hole 43 to. rest upon the spring look washer 45. The pilot member 45, or plug, performs the same function as the end portion 28 of the stud 2ii heretofore desaribecl.

If it is desired to replaae studs on exsting equipment, this arrangement aan he IJised. Also, the loose pilot or plug member 45 permits the use of the stud in relatively deep holes without the neaessity of making the pilot member integral with the stud. The, arrangement illustrated in Figure 3, also permits an adaptation of the prinaiples of this invention to studs that are used on exstng equiprnent because the stuols can be iethreadeal to an undersi2e aonditon comparable of that referred to in connection with the clesaription of the stud 20 and the loose pilot member 45 ha inserted in the hole so that the compression of the spring look washer 46 aan perorm its funation upon the stud 43 to retain the threads lii thereof in engagement with the threacls 42. Also, the stud that is being reworked aan have the shank portion thereof underaut in the Same marmer as the underaut portion 2, illustrated in Figure 1, i t having been founcl in practice that when the principles of this invention are applied to studs that, as a general rule, the diameter of the stud aan be reducecl beeause the loealized stresses have been remoVed from the stud.

In Figure i, there is shown a modifiecl arrangement or obtaining an angle thrust upon the stud 28 to force the upper aaes of the threads of the stud. into engagement with the 1ower faces of the threads in the tapped hole 24. In this arrangement a rubber plug 59, or a plug of material of a rubber like substance, suah as the syn 23 of the tapped hole 24, in the same marmer as heretofore described.

While the meahaniaal arrangement of the deviae disclosed and described herein aonstitutes a preferred form of the device, yet, it will be un-= clerstood that it is capable of mechanical alteration without departing from the spirit of the invention, and that all suah modifiaations as fall within the scope of the appended claims are intended to be included herein.

Having thus fully described n1y inventbn what I claim as new and desire to secure by Letters Patent is:

1. A stud fastening mchanism that inaludes a member having a threaded hole therein, a stud having a thread portion thereon reoeived in the threads of the threadeol hole, the alearanae between the threacls on the threacled portion of the stud ancl th threads in the hole beng greater than the maximum alearanae permitted between suah threads aaaording to the toleranaes allowed in standard thread practica whereby the threads on the stud are a relatively loose it in the threads in the hole as gauged by stanalard thread practiae, anti resilient means within the threaded. hole engagecl by the stud whereby to app1y an axial force upon the stud to aause riatonal engagement between one side of the threads on the stud and one sice of the threads in the hole.

2. A stud astenn meahanism that includes a member having a threacied hole therein, a stud having a threacl portion thereon reaeved in the threacls of the threadecl hole, the alearance between the threads on the threaded portion of the stud and the thraads of the hole exaeeding the maximum alearance permitted between suah threads aa-aording to the tolerances allowecl by standard. thread praatiae, whereby the threads on the stud are a relatively loose fit in the threads in the hole, reslient means within the th-reaced. hole engagecl by the stud whereby to apply an axial force upon the stud to cause friational engagement between one side of the threacison the stud and. one side of the threads in the hole, and a body portion of said stud in Juxtaposition to the 0 innermost thread of saial threaded. portion having a diameter not greater than the minor or root diameter of the threads thereon to prevent localization of stress at the root diameter of said. threads on said stud.

3. A stud fastening meahanism that includes a member having a threaded hole therein, a stud having a threac' portion thereon received in the threads of the threazied hole, the aiearanae be tween the threacls on the threadecl portion of the stud and the threads in the hole being greater than the maximum clearanae permitted between suah threads aacording to the tolerances allowed in standard thread praatice vvhereby the threads on the stud are a relatively loose fit in the threads in the hole, resilient means within the threadecl hole engaged by the stud whereby to app1y an axial forae upon the stud to cause frictional engagement between one side of the threads on the stud and one side of the threads in the hole, and a body portion of said. stud in juxtaposition to the innermost thread of said threaded portion having a diameter not greater than the minor or root diameter of the threads thereon and joined with the threaded portion of the stud by means of a chamfered stud body portion to prevent localization of stress at the root diameter of said threads on said stud.

4. Astud fastening device that-includes, a member having a threaded hole theren, a stud memallowed in standard thread practice whereby a relatively loose thread fit therebetween is provided as gauged by standard thread prctice thereby preventing localization of stresses in the stud at the first thread line in the stud adjacent said body portion, and resilient means within said threaded hole in said first member engaged by said stud for applying an axial force thereon to cause axial movement of the stud in the hole to place one side of the threads 011 the stud in frictional engagement with one side of the threads in said hole to thereby distrbute the stress load on the stud over all the threads thereof and prevent rotation thereof tending to remove the stud from the hole.

5. A stud fastening device that includes, a member having a threaded hole therein, a stud member having threads on an end portion thereof having a root diameter greater than the cliameter of the body portion of the stud in juxtaposition to the innermost thread thereon and which are undersize relatively to the threads in the hole in said first member that the clearance between the threads of the stud and the threads in the hole is greater than the maximum clearance permitted between such threads according to the tolerances allowed in standard thread practice wherby a relatively loose thread fit therebetween is provided as gauged by standard thread practica thereby preventing localization of stresses in the stud at the first thread line in the stud adjacent said body portion, and a spring look washer in said hole engaged by the bottom of said stud for applying an axial forse thereon to cause axial movement of the stud in the holeto place one side of the threads on the stud in frictional engagement with one side of the threads in said hole to thereby distribute the stress load on the stud over all the threads thereof and prevent rotation thereof tending to remove the stud from the hole.

6. A stud fastening device thatdncludes, a member having a threaded hole therein, a stud member having threads on an end portion thereof having a rootdiameter greater than the diameter of the body portion of th stud in juxtaposition to the innermost thread thereon and which are undersize relatively to the threads in the hole in said first member that the clearance between the threads of the stud and th threads in the hole is greater than the maximum clearance permitted between such threads according to the tolerances allowed in standard thread practice whereby a relatively loose thread fit therebetween is provided as gauged by standard thread practice thereby preventing localization of stresses inthe stud at the first thread line in the stud adjacent said body portion, said stud being positioned within said hole with the innermost thread on said stud disposed within said hole and below the surface of the member in which said hole is placed and with the bodyportion of the stud that is in juxta;position to said innermost threadout of contact with said member, and resilient means wthin said threaded hole insaid irst member engaged by said stud 10 or applying an axialforce thereon to cause axial movement of the stud in the hole to place one side of the threads on the stud.in frictional engagement with one side of. the threadsin said hole 'to thereby distrbute the stress load on the stud over all the threads thereof and prevent rotation thereof tending to remove the stud from the hole.

7. A stud fastening device that includes, a member having a threaded hole therein, a stud member having threads on an end portion thereof having. a root diameter greater than the di-- ameter of the body portion of the stud in juxtaposition to the innermost thread thereon and. which are undersize relatively to the threads in the hole in said irst member that the clearance between the threads of the stud and the threads in thehole is greater than the maximum clearance permitted between such threads according to the tolerances allowed in standard thread 39 practica whereby a relatively loose thread fit therebetween is provided as gauged by standard thread praetice thereby preventing looalization of stresses in the stud at the first thread line in the stud adjacent said body portion, resilient means within said hole beneath said stud, and

a pilot member between said resilient means and said stud whereby the expansiv orce of said resilient means urges said pilot member and said stud axially to cause frictional engagement be- 40 tween one sideof the threads on said stud and one side of the threads in said hole to thereby cause distribution of stress applied upon said stud over all the threads thereof and to prevent rotation of said stud tending to remove the same from said member.

8. A stud for receiving high axial stresses that consists of a stud body member, threads on an end portion of said body member that are undersize as gaugedby standard thread practica relatively to the threads of a hole that are adapted to receive the same so that the clearance between the stud threads and the threads in the hole with which they cooperate is greater than the maximum clearanoe permitted according to the tolerances allowed in standard thread practice, said stud body having a portion thereof adjacent the innermost thread provided with a diameter not greater than the root diameterof said threads, whereby said body portion will be 6 disposed out of engagement with the threads in a hole that is adapted to receive said stud and prevent localizati0n of stress in the stud at the thread line thereof.

9. A stud or receiving high axial stresses that consists of a stud body member, threads on an end portion of said body member that are under size as gauged by standard thread practica relatively to the threads of a hole that are adapted to receive the same so that the clearance between the stud threads and the threads in the hole with which they cooprate is greater than the maximum clearance permitted according to the tolerances allowed in standard thread practice,

said stud body having a portion thereof aoljacent the innermost thread provided with a diameter not greater than the root diameter of said threadg and contiguous with said innermost thread by a chamfered body portion extending therebetween, whereby said body portiun Will be disposed out of engagement with the threads in a hole that is adapted to receive said stud and prevent localization of stress in th stud at the thread 1ne thereof.

10. A stud fastening mechanism that includes a member having a threaded hole theren, a stud having a threaded portion thereon receved in the clearance between the threads of the threaded hole, the threads on the threaded Dortion of the stud and the threacls in the hole being greater than the maximum clearance permitted between such threads according to the tolerances allowed in standard thread practica whereby the threads on the stud are a relatively loose fit in the threads in the hole as gauged by standard thread practce, a member extending from the end of said stud toward the bottom of said hol having a diameter less than that of said hole, a member of rubber like materal disposed within the threaded hole and engaged by said member extending from said stud to compress the rubber like material between said extending member and said hole to thereby apply an axial forse upon the stud to cause frictional engagement betwen one side of the threads on the stud and one side of the threads in the hole and also frictionally resist rotation of said stud.

11. A stud astenin mechanism that includes a member having a threaded hole therein, a stud having a threaded portion thereon received in the threads of the threaded hole, the Clearance between the threads on the threaded portion of the stud and the threads in the hole being greater than the maximum clearance permitted between such threads according to the tolerances allowed in standard thread practice whereby the threads on the stud are a relatively loose fit in the threads in the hole as gauged by standard thread practice, a member extending from the end of said stud toward the bottom of said hole having a diameter less than that of said hole, a member of rubber like material disposed wthn the threaded hole and engaged by said member extending from said st-ud to compress the rubber lke material between said extending member and said hole to thereby apply an axial force upon the stud to cause irictional engagement between one side of the threads on the stud and one side of the threads in the hole and also frictonally resst rotation of said stud, and a body portion on said stud in juxtapostion to the innermost thread of said threaded portion having a diameter not greater than the minor or root diameter of the threads thereon to prevent localization of stress at the root diameter of said thread on said stud.

12. A stud fastening mechanism that includes a member having a threaded hole therein, a stud having a threaded portioii thereon received in the threads of the threaded hole, the Clearance between the threads on the threadea portion of the stud and the threads in the hole being greater than the maximum clearance permitted between such threads according to the tolerances allowed in standard thread practioe whereby the threads on the stud ar a relatively loose fit in the threads in the hole as gauged by standard thread praotce, a member extending from the end of said stud towardthe bottom of said hole having a diameter less than that of said hole, a member of rubber like material dsposed wthin the threa'ded hole and engaged by said member eXtending from said stud to compress the rubber like material between said extending member and said hole to thereby ap;ply an axial force upon the stud to cause frictional engagement between one side of the threads on the stud and one side of the threads in the hole and also frictionally resist rotaton of said stud, and a body portion on said stud in juxtaposition to the innermost thread of said threaded portion having a diameter not greater than the minor or root diameter of the threads thereon and joined With the threaded portion of the stud by means of a curved stud body portion to prevent looalization of stress at the root diameter of said thread on said stud.

OTTO M. SUMMERS. 

